KABUL (Reuters) -- More British than U.S. soldiers have been killed in Afghanistan in the past six weeks, despite America having four times more troops in the country.

The steadily rising death toll comes as violence in Afghanistan has reached its highest levels since 2001, with Afghan and foreign forces locked in daily battles with an increasingly deadly and resilient Taliban insurgency.

Some 4,000 people, one-third of them civilians, were killed in the first half of this year alone.

Since the beginning of November, 12 British soldiers have died, compared to only three U.S. soldiers in the same period, according to U.S. and British military statements. Three British soldiers were killed in a single suicide bomb blast.

A spokesman for the NATO-led force in Afghanistan said increased engagements and the tactics used by insurgents, such as roadside bombs and suicide attacks, were to blame, but the rise in British casualties could be attributed to no one cause.

"Over the past few weeks, the Brits have been engaging the enemy pretty hard. If you engage the enemy, you come into contact with them," said British Navy Captain Mark Windsor.

"We've been having a bad time. I don't think there's any specific reason for it, apart from the fact that it's tough down there," he said, referring to Helmand, a province in southern Afghanistan where the Taliban have a strong presence.

Since the Taliban were toppled in 2001, the U.S. military has suffered more casualties than all the other 40 foreign countries with troops in Afghanistan put together, but it also now has nearly half the 65,000 international soldiers there.

The number of British soldiers to have died since 2001 is 133, compared to 629 from the U.S. military. The U.S. has 31,000 U.S. troops based in Afghanistan, while Britain has 8,300, making it the second-highest force-contributing nation.

The latest British soldier to die was hit by insurgent gunfire on December 15 at a base in Helmand. Forty-seven British soldiers have died this year, more than one-third of total British fatalities since 2001.

No Protection

One criticism leveled at the British military is that it uses insufficiently armored vehicles to protect its soldiers on patrol, making them vulnerable to roadside bombs.

Thirty-seven British soldiers have been killed in Iraq and Afghanistan while traveling in lightly armored "Snatch" Land Rovers, the most commonly used troop-carrying vehicle.

Despite that heavy death toll, the Ministry of Defense said it would go on using the vehicles, despite persistent concerns raised by troops about their safety, while gradually introducing a slightly better protected version of it.

A retired British officer said that if British troops wanted to stay close to the Afghan people, and win them over, they would always face risks from mines and suicide bombers. And he said better armored vehicles wouldn't necessarily work.

"There is almost no protection against a serious amount of plastic explosive," Colonel Bob Stewart, former commander of UN forces in Bosnia, told Reuters.

"If there is a requirement for British soldiers to be out on the ground with the population, doing the hearts-and-minds stuff, which there is, then there is going to be a greater risk," he said.

The number of wounded British soldiers has also reached its highest levels, with 59 troops very seriously or seriously wounded in the first 11 months of this year, Britain's Defense Ministry said.

In 2007, 63 British soldiers were seriously wounded, and only four were killed during all of November and December.

While the cold winter months in Afghanistan usually see a drop in fighting, U.S. military commanders have said there will be no letup this winter in the battle with Taliban insurgents.